CO2 laser may be used for laser produced plasma (“LPP”) extreme ultraviolet (“EUV”), i.e., below about 50 nm and more specifically, e.g., at around 13.5 nm. Such systems may employ a drive laser(s) to irradiate a plasma formation material target, e.g., target droplets formed of a liquid containing target material, e.g., molten metal target material, such as lithium or tin.
CO2 has been proposed as a good drive laser system, e.g., for tin because of a relatively high conversion efficiency both in terms of efficiency in converting laser light pulse photon energy into EUV photons and in terms of conversion of electrical energy used to produce the drive laser pulses for irradiating a target to form a plasma in which EUV light is generated and the ultimate wattage of EUV light generated.
Applicants propose an arrangement for delivering the drive laser pulses to the target irradiation site which addresses certain problems associated with certain types of drive lasers, e.g., CO2 drive lasers.
Pre-pulses from the same laser as the main pulse (e.g., at a different wavelength than the main pulse may be used, e.g., with a YAG laser (355 nm—main and 532 nm—pre-pulse, for example). Pre-pulses from separate lasers for the pre-pulse and main pulse may also be used. Applicants propose certain improvements for providing a pre-pulse and main pulse, particularly useful in certain types of drive laser systems, such as CO2 drive laser systems.
Applicants also propose certain improvements to certain types of drive lasers to facilitate operation at higher repetition rates, e.g., at 18 or more kHz.